Connected heat conducting structures in solid ammonia storage systems

ABSTRACT

A compacted block of material constructed of one or more units consisting of matter comprising an ammonia-saturated material capable of reversibly desorbing and ad- or absorbing ammonia surrounded by a gas-permeable enclosure made of a flexible material having a thermal conductivity of at least about five times the thermal conductivity of said ammonia-saturated material at −70° C.. to 250° C.. and methods for producing the same are described.

FIELD OF THE INVENTION

The invention relates to a compacted block of material constructed ofone or more units consisting of matter comprising an ammonia-saturatedmaterial surrounded by gas-permeable, flexible heat conducting materialand a method for producing it.

BACKGROUND OF THE INVENTION

Ammonia is a widely used chemical with many applications. Specificapplications include using ammonia as reductant for selective catalyticreduction (SCR) of NO_(x) in exhaust gas from combustion processes orusing ammonia as fuel in energy generating processes as for example inrelation to fuel cells.

For most applications, and in particular in automotive applications, thestorage of ammonia in the form of a pressurized liquid in a vessel istoo hazardous. Urea is a safe, but an indirect and impractical methodfor mobile transport of ammonia since it requires urea to be transformedinto ammonia by a process involving thermolysis and hydrolysis((NH₂)₂CO+H₂O→2NH₃+CO₂).

A storage method involving ad- or absorption in a solid can circumventthe safety hazard of anhydrous liquid ammonia and the decomposition of astarting material.

Metal ammine salts are ammonia absorbing and desorbing materials, whichcan be used as solid storage media for ammonia (see, e.g. WO 2006/012903A2), which in turn, as mentioned above, may be used as the reductant inselective catalytic reduction to reduce NO_(x) emissions.

Ammonia release from the ammonia storage materials is an endothermicprocess that requires supply of heat. An associated problem is that thestorage materials and especially the ammonia depleted storage materialsin general have low thermal conductivity and upon depleting ammonia fromthe material porosities may form, which inhibit heat conduction evenmore. The effects of deteriorating heat conduction are that the heatingsource has to be heated to higher temperature and the response time ofthe system becomes longer.

Another problem arises from material properties changing upon depletionof ammonia from the ammonia storage materials. Because ammonia is asubstantial part of the structure of the materials, mostammonia-absorbing solids shrink in overall dimensions upon depletion. Ifthe material initially completely fills a container, it will loosecontact with the container walls after degassing. The gap between thecontainer wall and the storage material will act as an insulation layerand prevent heat being transported into the storage material if thecontainer is heated from the outside. It is also undesirable to have alarge block of material loosely contained in a container which ismounted on a moving and vibrating vehicle, as this may compromise themechanical stability of the system.

The present invention addresses these problems.

SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a compacted block ofmaterial constructed of one or more units consisting of mattercomprising an ammonia-saturated material capable of reversibly ad- orabsorbing and desorbing ammonia surrounded by a gas-permeable, flexiblematerial having a thermal conductivity of at least five times thethermal conductivity of said ammonia-saturated material at −70° C.. to250° C..

In a second aspect, the invention relates to a method of producing thecompacted block of material comprising:

-   wrapping said matter comprising an ammonia-saturated material    capable of reversibly ad- or absorbing and desorbing ammonia into a    gas-permeable, flexible material having a thermal conductivity of at    least five times the thermal conductivity of said ammonia-saturated    material at −70° C.. to 250° C.. so that one or more units of    wrapped matter are provided,-   and compressing said one or more units by an external pressure of at    least 5 MPa, wherein optionally said one or more units are placed in    a container or mold having one or two open ends and optionally one    or more removable walls and said external pressure is exerted    uni-axial through the open end(s), optionally via a plate.

In a third aspect the invention relates to a method of producing thecompacted block of material comprising:

-   wrapping matter comprising an ammonia-depleted material capable of    reversibly ad- or absorbing and desorbing ammonia into a    gas-permeable, flexible material having a thermal conductivity of at    least five times the thermal conductivity of said ammonia-saturated    material at 70° C.. to 250° C.. so that one or more units of wrapped    matter are provided,-   filling the one or more units into a container, such that the    unit(s) are immobilized in the container, and-   saturating the ammonia-depleted material capable of reversibly ad-    or absorbing and desorbing ammonia with ammonia.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an ammonia storage material in a container eachportion thereof surrounded by an enclosure of a gas-permeable, flexible,heat conducting material thus forming storage material-containing unitsor packages the enclosures forming a connected structure of closedsurfaces.

FIG. 2 illustrates an ammonia storage material in a container surroundedby one enclosure of a gas-permeable, flexible, heat conducting materialwherein the enclosure, besides the ammonia storage material, enclosessecondary storage material-containing units the enclosures of which donot form a completely connected structure of closed surfaces.

FIG. 3 illustrates a method of forming the structure of FIG. 1 usingexternal force or pressure.

FIG. 4 illustrates a method of forming the structure of FIG. 1 usingsaturation of the material inside a container.

FIG. 5 schematically shows a production line for the ammonia storagematerial packages wrapped into gas-permeable heat conducting flexiblefoil.

FIG. 6 shows the temperature/pressure curves of the phase boundary ofliquid ammonia/gaseous ammonia and of the equilibrium pressure ofSr(NH₃)₈Cl₂.

DESCRIPTION OF THE EMBODIMENTS

The present invention solves the above-mentioned problems by enclosingthe ammonia storage material capable of reversibly ad- or absorbing anddesorbing ammonia inside one or more enclosures. The enclosure consistsof or comprises a heat conducting material that is permeable for gastransport but not for the storage material. The enclosures act as heattransfer structures parallel to the enclosure surface. The enclosuresare packed or compacted to leave vanishing or substantially no void orinterstices between adjacent enclosures. In this way the enclosures areconnected to neighboring enclosures through a large area giving almostno heat flow resistance between neighboring enclosures. In effect a heatconducting structure consisting of a fully connected set of closedsurfaces with maximum heat transfer capability is obtained.

Thus, in one aspect the invention relates to a compacted block ofmaterial constructed of one or more units consisting of mattercomprising an ammonia-saturated material capable of reversibly ad- orabsorbing and desorbing ammonia surrounded by a gas-permeable, flexiblematerial having a thermal conductivity of at least five times thethermal conductivity of said ammonia-saturated material at −70° C.. to250° C.., i.e. over the whole range of −70° C.. to 250° C..

“Compacted block of material”, as used herein, means a mass of materialhaving the gross of appearance of a block of any desired shape, such asa cylinder, a cube, an ashlar, a pyramid etc or also a totally irregularshape, which is compacted or compressed. The block consists of one ormore units (or “packages”), usually of more than one unit (e.g., atleast about two, three, four, five, six, seven, eight, nine, ten,fifteen, twenty, fifty, or hundred units), that can individually beidentified since each unit is surrounded by an enclosure or closedsurface of “wrapping” material. The material within the enclosurecomprises one or more materials capable of ad- or absorbing anddesorbing ammonia, in its ammonia-saturated state.

Thus, the material(s) capable of ad- or absorbing ammonia (“ammoniastorage material”) is (are) physically divided into enclosedcompartments within the block. Since the block is compacted orcompressed the major part of each enclosure is in contact with aneighboring enclosure. The voids or interstices between the enclosuresof the packages, i.e. the interfaces between the enclosures, are reducedto a minimum, i.e. the voids occupy equal to or less than about 15%,10%, preferably less than about 5%, such as less than 2% or 1% by volumeof the volume of the block of material. The contacting surface areas actas a heat transfer area, and the thermal contact resistance vanishes aslong as the thickness of the enclosures is small compared to the size ofthe enclosures. As a result, the enclosures form a completelyinterconnected set of closed surfaces that act as a heat transferstructure between any two parts of the block.

The large contact area between neighboring enclosures, which is a resultof the compaction or compression, furthermore leads to mechanicalstability of the overall structure or block that is robust vis-à-vis themechanical deformations of the ammonia storage material upon desorptionor degassing of ammonia.

When there are more than one unit present in the block, there may be anouter enclosure heat conducting gas-permeable, flexible material asdefined above surrounding all units. The more than one enclosures cancomprise the same or different heat conducting materials and can enclosethe same or different ammonia storage materials. For example, in themore than one units Sr(NH₃)₈Cl₂ may be contained in an enclosure made ofaluminum and Ca(NH₃)₈Cl₂ may be contained in an enclosure made of analuminum alloy.

The number of units or packages, and thus of the enclosures, as well asthe size and shape of the units or packages, and thus of enclosures, andthe material of the enclosures may vary widely, even within one specificcompacted block. Because the block has been compacted or compressed, theresulting final shape of the units and enclosures is not uniform, butwill, depending on the initial package shape and exact position of thepackages before compressing vary stochastically. However, since theratio of ammonia storage material to enclosure material is well definedon the package scale, the statistical variations are small particularlywhen the starting sizes of the packages are similar. Therefore, onlength scales larger than the package size the mean values ofcomposition and thermal behavior are well defined. Therefore, there isno need in the production process, as described hereinafter to havedetailed control of the material positions.

Although not being limited thereto, a typical dimension of the startingunits or packages will be about 1 cm to about 10 cm in diameter,preferably about 5 cm to about 10 cm for use in a container or cartridgehaving a diameter of from about 10 cm to about 30 cm, and about 2 cm toabout 6 cm for a use in a container or cartridge smaller than 10 cm indiameter.

The flexible material surrounding the matter comprising the ammoniastorage material, usually some kind of foil or film, is gas-permeable,but substantially dust-tight (i.e. substantially impermeable for theammonia storage material). The gas permeability is necessary to ensuregas passage from the ammonia storage material when the latter isdesorbed or degassed. The property of dust-tightness prevents that theammonia storage material enters the initial voids and intersticesbetween the packages and any container walls, if present, during themanufacturing process which otherwise would result in a greatlyincreased thermal contact resistance and decreased mechanical strengthof the final block structure. Furthermore, a loss of ammonia storagematerial and ammonia is reduced during processing.

The necessary gas permeability and dust tightness can be achieved byusing a porous foil or film, by perforating the foil or film beforeforming the packages, by using a foil or film which will becomegas-permeable, e.g. porous or perforated, during the compressionprocedure or simply by closing the packages in a non-hermetical manner.For example, a standard non-permeable foil that is simply wrapped aroundthe ammonia storage material in an overlapping manner to form a packageusually has sufficient leak in the enclosure of the package for anammonia gas transport out of the package but without allowing powder toescape. By gas-permeable the possibility of ammonia gas transport out ofthe packages by any of the above mentioned mechanisms or any othersuitable mechanism leading to the same performance is meant.

The thickness of the foil or film is not critical, as long as it issmall compared to the dimension of the whole unit or package. Ingeneral, the thickness may vary from about 1 μm to about 100 μm,preferably from about 10 μm and to about 50 μm.

Any enclosure made of a material that can be made flexible andgas-permeable and has a thermal conductivity of at least about fivetimes, preferably about ten times, and even about 20, about 50 or about100 times the thermal conductivity of the ammonia-saturated storagematerial at −70° C.. to 250° C.. may be used in the present invention.Exemplary materials are or comprise metal, metal alloys, graphite,composite materials, e.g. plastics that has been modified to be heatconductive, rubber that has been modified to be heat conductive, and anymixtures thereof. Also contemplated are composites of a heat conductingmaterial, as defined above, and a material having a lower thermalconductivity, as long as the overall thermal conductivity is as definedabove for the heat conducting materials. Preferably, the materials havegood mechanical strength and are inert towards ammonia. Presentlyparticularly preferred materials are aluminum and aluminum alloys.

For example, the thermal conductivity of aluminum is about 240 W/mK,that of aluminum alloys is somewhat smaller. Generally, most metals havea thermal conductivity of the same order.

In contrast, the thermal conductivity of storage material made of metalammine salts is in the order of about 1 W/mK.

The heat conductive gas-permeable enclosure made of a flexible materialusually comprises at least about 0.1 mass %, e.g. about 2 mass %, about5 mass %, about 20 mass % and not more than about 20 mass % of the massof the compacted block.

If the compacted block is contained in a container, the heat conductivegas-permeable, flexible material usually comprises at least about 0.1vol. % and not more than about 10 vol. % of the container volume.

The number of enclosures, the enclosure sizes and shapes and the thermalconductivity and thickness of the enclosures all affect the overallthermal performance of the compacted block. For two blocks having thesame amount and type of enclosure material and ammonia storage material,but different numbers of enclosures, the enclosure sizes and surfaceareas will, of course, be different. The smaller the number of units andenclosures the larger is the size of the units and enclosures, and theaverage distance between enclosure surfaces and ammonia storage materialhaving poor heat conductivity will be larger. For specific applications,the above-mentioned parameters are usually optimized to give the desiredoverall thermal conductivity and thermal response time.

The above-described heat conductive gas-permeable enclosure made of aflexible material serves as an enclosure of matter that comprises anammonia-saturated material capable of reversibly desorbing and ad- orabsorbing ammonia (“ammonia storage material”).

Examples of materials capable of reversibly desorbing and adsorbingammonia are ammonia-saturated acid-treated carbon and zeolites.

Examples of materials capable of reversibly desorbing and absorbingammonia are metal ammine complex salts and are preferably selectedtherefrom or comprise the same. Preferred metal ammine complex salts areof the formula M_(a)(NH₃)_(n)X_(z), wherein M is one or more cationsselected from alkali metals such as Li, Na, K or Cs, alkaline earthmetals such as Mg, Ca, Sr or Ba, and/or transition metals such as V, Cr,Mn, Fe, Co, Ni, Cu, or Zn or combinations thereof, such as NaAl, KAl,K₂Zn, CsCu, or K₂Fe; X is one or more anions selected from fluoride,chloride, bromide, iodide, nitrate, thiocyanate, sulphate, molybdate,and phosphate ions; a is the number of cations per salt molecule; z isthe number of anions per salt molecule; and n is the coordination numberof 2 to 12, preferably 6 to 8.

Metal ammine salts selected from or comprising Mg(NH₃)₆Cl₂, Ca(NH₃)₈Cl₂,Mn(NH₃)₆Cl₂ and Sr(NH₃)₈Cl₂ and any mixture thereof are particularlypreferred.

Metal ammine complex salts are formed from the plain ammonia-freestarting salt by a variety of methods well-known to the person skilledin the art, such as saturation of the plain starting salt in anatmosphere of ammonia e.g. in a container or rotating drum or bytreating the plain starting salt with liquid ammonia.

In the context of the present invention “ammonia-saturated” meansmaterial capable of reversibly ad- or absorbing and desorbing ammoniawherein most or sometimes virtually all of the sites in the materialthat can be occupied by ammonia are occupied thereby. In most cases astoichiometrically complete saturation is difficult or impossible toachieve and that therefore the term “ammonia-saturated” includes thehighest degree of saturation that can reasonably achieved practicallybut does not correspond to the stoichiometric full saturation, i.e. asaturation degree of at least about 80% or 85%, more preferably at leastabout 90 or 95%, e.g. at least about 97% or 98% or even 99% of thetheoretical full saturation.

If the ammonia-saturated material consists of one or more of theabove-described ammonia-saturated metal ammine salts, its is preferredthat the compacted block of material has been compacted such that thedensity of the ammonia-saturated metal ammine salt(s) is at least about70% of the maximum density thereof. By “maximum density” that density ismeant, which the saturated metal ammine salt would have, if it were asingle crystal at ambient temperature and pressure. More preferred is adensity of at least about 75%, or about 80%, or about 85%, or about 90%,or about 93%, or about 95% or about 97% even more than about 97% of themaximum density.

The matter which is surrounded by the heat conductive gas-permeableflexible material, besides comprising the ammonia-saturated storagematerial, may also comprise additives, such as binders, but inparticular heat conducting particles and coherent heat conductingstructures. The heat conducting particles (e.g. flakes, pellets etc.)and coherent structures (such as small grids etc.) may be made of thesame materials as the above-mentioned materials that may be madegas-permeable and flexible. The amount of such additives is usually inthe range of about 1.5% or 2% by volume to about 10% by volume of thevolume of the ammonia storage material.

If there is present only one unit, as defined above, this “primary”unit, besides “unpackaged” material capable of ad- or absorbing ammoniaand possible additives and/or coherent heat conducing structures,usually contains smaller secondary units or packages which are otherwiseidentical to the ones defined above. However, such secondary units mayalso be enclosed, when more than one of the above-identified primaryunits or packages are present. The secondary units usually have a sizeof about 5% by volume to about 50% by volume of the volume of thesurrounding primary units.

The compacted blocks have been compressed by means of such a pressure orforce that they reach a degree of compaction where the voids andinterstices of the non-compacted starting assembly of packages or unitshave disappeared to a large extend. Often the starting assembly iscompacted to the maximum degree where it cannot be compressed anyfurther. Although the pressure applied to cause the voids andinterstices of the starting assembly to disappear varies with the natureof the ammonia-saturated material, a minimum pressure is often about 5,or more, such as about 10, about 20, about 50, about 100 or even about200 MPa or more.

The compacted block of material of the present invention may beself-supporting, i.e. keep its shape even when it is not enclosed in anouter container. In this case, the compaction can be achieved e.g. byapplying pressure from all sides of the starting assembly of the units.More usually, the starting assembly of the compacted block of materialis introduced into some kind of container, e.g. a cylinder mead ofsteel, having one open end or two opposite open ends and which canwithstand high pressures and then uni-axially compressed, often via oneor two plates placed onto the starting assembly. Optionally, the wall ofthe container can be removed so as to take out the compacted block ofmaterial.

The self-supporting block of material may then be introduced into acontainer which optionally can be heated in order to release ammoniafrom the ammonia-saturated material, generally at a temperature of about40° C.. to about 200° C.. at an ammonia pressure of about 2 bars toabout 5 bars. The heating of the container may be external or internal.In the former case, the container is preferably heat conducting, e.g.made of a material such as aluminum, steel or other metal alloys havinga high thermal conductivity. However, it is also possible to use vacuumto release the ammonia or a combination of heat and vacuum. For example,in the case of a vacuum of about 0.5 bar the ammonia desorption takesplace at about room temperature (about 25° C.).

Alternatively, the starting assembly can be placed into the finalcontainer from which the ammonia is released which optionally which hasat least one and usually just one open end and can be heated in the sameway as mentioned above. However, in this case the container must be ableto withstand the pressure required to compact the material or it isplaced into a mould with sufficient strength to mechanically support thecontainer during pressing. The starting assembly of the material forforming the compacted block is then uni-axially compacted within thiscontainer.

It is preferred that at most about 20% of the total enclosure area isperpendicular within about ±10° to the desired direction of heattransport, or that at least about 80% of the total surface area of saidgas-permeable, flexible materials is parallel within about ±10° to thedesired direction of heat transport.

The desired direction of heat transfer is usually equivalent to thedirection of the heat flux if no heat conduction improving structures oradditives are present. The heat flux can be found by mathematically(analytically or numerically) solving the heat conduction problem forthe given configuration of container and heat supply. For example for aconfiguration with cylindrical symmetry around an axis, the desireddirection of heat transfer is perpendicular to the symmetry axis. Formore complex geometries the heat flux in absence of heat conductingstructures and hence the desired direction of heat transfer willgenerally be a function of position. Thus the desired direction of heattransfer in any given point in the container is defined as the directionof the heat flux if no heat transfer improving structures were present.

However, due to the stochastic nature of the connected set of heatconducting surfaces it is not possible to align all the heat conductingmaterial exactly along the desired direction of heat transfer. Thus itis preferred that at least about 60% of the heat conducting material isaligned within about ±20° to the desired direction of heat transfer. Itis more preferred that at least about 80% of the heat conductingmaterial is aligned within about ±20° to the desired direction of heattransfer. It is even more preferred that at least about 80% of the heatconducting material is aligned within about ±10° to the desireddirection of heat transfer.

Further, due to the stochastic nature of the connected set of heatconducting surfaces it is not necessary to exactly know the desireddirection of heat transfer and often it can be approximated by somesuitable simple method. For example the desired direction of heattransport at a given point in the container could be approximated by thedirection of the shortest line connecting the heating element to saidgiven point.

For a configuration with cylindrical symmetry the approximated directionwill be exact. In this case, the desired direction of heat transport isalong a radius starting from the longitudinal axis through the center ofmass of the compacted block, and, preferably, at most about 20° of thetotal area of the enclosures is perpendicular within about ±10° to suchradius. This may be achieved e.g. by an oval shape of the starting unitsor packages and/or by uni-axial compression.

In the case described above, most of the total enclosure surface isparallel to the desired direction of the heat transport: Then thecorresponding overall thermal conductivity in the desired direction canbe estimated as the weighted average of the thermal conductivities ofthe enclosure material(s) and the storage material(s).

In an example, in which the enclosure material is aluminum with athermal conductivity K_(e)=240 W/mK, the ammonia storage material hask_(s)=1 W/mK and the enclosure material comprises 2.5% of the containervolume in which it is contained, the estimated overall thermalconductivity is 0.025 K_(e)+0.975 k_(s)=7 W/mK, Preferably, the overallthermal conductivity ranges from 1 W/mK to 20 W/m K.

In a further aspect, the invention relates to a method of producing thecompacted block of material as described above comprising:

-   wrapping said matter comprising an ammonia-saturated material    capable of reversibly ad- or absorbing and desorbing ammonia into a    gas-permeable, flexible material having a thermal conductivity of at    least five times the thermal conductivity of said ammonia-saturated    material at −70° C. to 250° C. so that one or more units of wrapped    matter are provided,-   and compressing said one or more units by an external pressure of at    least 5 MPa, wherein, optionally, said one or more units are placed    in a container or mold having one or two open end(s) and optionally    one or more removable walls and said external pressure is exerted    uni-axial through the open end(s), optionally via a plate.

The wrapping procedure should be fast, robust and reproducible. It is anadvantage, if the wrapped packages have a shape that is easy to handleand that packs evenly, when the packages are poured in the containerbefore pressing. Often an almost spherical shape is preferred. It isfurther an advantage, if the material is pre-compacted in the wrappingprocess. Preferably, the material is pre-compacted to about ⅓ of thefinal density. Even more preferred is a pre-compaction to about ½ of thefinal density. An example of an automated wrapping sequence isillustrated in FIG. 5. First a piece of aluminum foil is formed into abowl shape in a shaping tool. Then, the bowl shape is filled with apredetermined amount of ammonia-saturated storage material. Thereafter,the bowl shape is pre-closed by pressing the edges of the bowl shapetogether. Finally, the package is closed and pre-compacted by pressingwith an inverted bowl shaped piston from above and thereafter removedfrom the packing line. The bowl shape can be varied to give differentpackage shapes, for example a hemi-spherical shape to produce sphericalpackages.

Then the material is simply introduced (“poured”) into the container ina manner similar to that of introducing bulk or granulated or powdermaterial.

Subsequently, the material is compressed or compacted by means of anexternal pressure of at least about 5 MPa, more preferred at least about10 MPa, e.g. about 20 MPa, about 50 MPa, about 100 MPa, about 200 PPa oreven more than about 200 MPa. The compression may be from all sides ofthe assembly of wrapped unit(s) or package(s) e.g. in a chamber havingsuitable movable walls onto which a force may be applied.

More usually, the assembly of wrapped packages is compresseduni-axially, as described above. On this manner it can be achieved thatnot more than 20° of the total area of the enclosures is perpendicularto the desired direction of heat conductance.

If the ammonia-saturated material consists of one or more of theabove-described ammonia-saturated metal ammine salts, its is preferredthat it is compacted such that the density of the ammonia-saturatedmetal ammine salt(s) is at least about 70% of the maximum densitythereof. By “maximum density” that density is meant, which the saturatedmetal ammine salt would have, if it were a single crystal at ambienttemperature and pressure. More preferred is a density of at least about75%, or about 80%, or about 85%, or about 90%, or about 93%, or about95% or about 97% even more than about 97%.

In a still further aspect the invention relates to a method of producingthe compacted block of material in a container, as described above,comprising: wrapping matter comprising an ammonia-depleted materialcapable of reversibly ad- or absorbing and desorbing ammonia into agas-permeable, flexible material having a thermal conductivity of atleast five times the thermal conductivity of said ammonia-saturatedmaterial at −70° C. to 250° C. so that one or more units of wrappedmatter are provided,

-   filling the one or more units into a container, such that the    unit(s) are immobilized in the container, and-   treating the ammonia-depleted material capable of reversibly ad- or    absorbing and desorbing ammonia with ammonia, thereby saturating and    compacting the material capable of reversibly ad- or absorbing and    desorbing ammonia.

In this method, the starting matter comprising the ammonia-depletedmaterial, loosely wrapped into the enclosures so as to leave enoughspace for an expansion of the material.

Ammonia-depleted material capable of reversibly ad- or absorbing anddesorbing ammonia means a material wherein the sites that can bindammonia are occupied only to a small degree (e.g. to a degree of lessthan about 20%) or not at all by ammonia. In the case of metal saltsthat can form metal ammonia complex salts, the plain metal salts may beutilized as a starting material.

The wrapped material is then placed into a container so that it cannotbe move therein (which is usually also achievable by mere “pouring” intothe container).

Then ammonia is introduced into the container either in gaseous or inliquid form so as to saturate the material with ammonia. It iswell-known to the person skilled in the art that ammonia-depletedstorage material expands upon saturation. In the present case, theammonia storage material, when enclosed in the container, will expand sothat voids and interstices between the units or packages and thepackages and the wall of the container diminish or disappear and theammonia storage material in its enclosures will eventually be pressedagainst the container wall, thus forming a compacted block of material.

In the above case, the amount of ammonia-depleted material filled intothe gas-permeable foil is such that after saturation with ammonia thematerial completely fills the package formed by the foil. This caneasily be calculated by means of the weight proportion of plain salt inthe saturated salt. For example, Sr(NH₃)₈Cl₂ contains 54% SrCl₂ byweight, so if a package should contain 100 g of Sr(NH₃)₈Cl₂ in the finalcompressed state, it should be filled with 54 g of SrCl₂.

In a particularly preferred embodiment, saturating and compacting thematerial capable of reversibly ad- or absorbing and desorbing ammoniacomprises:

-   a. placing the storage container(s) in direct or indirect contact    with a thermostatting medium at a temperature level T_(T)≦about 65°    C., and-   b. connecting the storage container(s) to a source of gaseous    ammonia wherein at least during a part of the saturation process the    gaseous ammonia during saturating of the ammonia storage material to    a predetermined saturation degree is at a pressure P_(S)≦about    P_(T), wherein P_(S) is the ammonia pressure during saturating of    the ammonia storage material and P_(T) is the equilibrium vapor    pressure of liquid ammonia at the temperature level T_(T).

The container may be in direct or indirect contact with thethermostatting medium in its entirety or only a part of the container isin direct or indirect contact with the thermostatting medium.

This method is described in detail for the similar re-saturation ofammonia storage material in the co-pending European patent applicationno. 10 005 245.5 the disclosure of which is expressly referred to.

In this method the temperature level T_(T) is preferably of from about0° C. to about 40° C., such as from about 0° C. to about 20° C. or fromabout 20° C. to about 40° C., the pressure P_(S) is preferably at leastabout 50%, such as at least about 75% or at least about 90% of theequilibrium vapor pressure of liquid ammonia at the temperature T_(T),and the predetermined saturation degree is preferably at least about80%, about 90%, about 95% or about 98%.

The thermostatting medium may be water or a monophasic aqueous medium.

The part of the method where the gaseous ammonia is at a pressure P_(S)which is lower than or equal to the equilibrium vapor pressure P_(T) ofliquid ammonia at the temperature T_(T) is preferably the final part ofthe method during the last about ⅓ of the total saturation period orwherein the last about 25% of the predetermined saturation degree isachieved.

It is preferable to avoid slow saturation at the end of the containeropposite to the ammonia inlet, since otherwise the storage materialclose to the ammonia inlet may be saturated at a faster rate than thestorage material at the opposite end of the container and the saturationof the storage material at the end of the container opposite to theammonia inlet may be impeded.

This can be controlled in several ways. In some embodiments, the part ofthe container or cartridge close to the ammonia inlet is insulated, e.g.about 50% or less, about 25% or less or about 10% or less, such as about5% or even less, of the surface of the cartridge may be covered with aninsulating material during part of or the whole saturation time. In someembodiments about 50% of the surface is covered in the beginning theprocess and then less and less surface is covered during the progress ofsaturation,

In some embodiment the thermostatting medium is applied only at the endof the cartridge opposite to the inlet, so as to increase the saturationspeed in that part of the cartridge. The level of the thermostattingmedium in thermostatting bath may furthermore be increased withincreasing saturation, starting at the end away from the ammonia inlet,until it completely covers the cartridge at the end of the saturationprocess. Another way of controlling the saturation speed is to providefor a temperature or heat dissipation gradient in the thermostattingmedium from colder at the end of the cartridge further away from theinlet to warmer at the end with the inlet, e.g. cooling the lower partof the container with the thermostatting medium more than the upper partand/or by flowing the thermostatting medium at a higher rate past thecartridge at its bottom part opposite to the inlet than past the upperpart with the inlet.

Furthermore, it is also possible to reduce the density of the storagematerial inside the container for controlling the saturation speed, if ahigh density is not so important.

These measures can lead to a saturation speed which is about the same inall parts of the cartridge or somewhat faster in the parts away from theammonia inlet.

Accordingly, in some embodiments of the method the direct or indirectcontact with the thermostatting medium is increased with increase ofsaturation or re-saturation by raising the level of the thermostattingmedium in a thermostattting bath in which the container is immersed,starting from the end of the container which is not connected to thesource of gaseous ammonia to the end connected to the source of gaseousammonia. Furthermore, the end of the container connected to the sourceof gaseous ammonia may be insulated such that about 50% or less, about25% or less or about 10% or less, such as about 5% or even less, of thesurface of the container is covered with an insulating material duringat least a part of saturation or re-saturation time. In someembodiments, a cooling device and/or other temperature controllingdevice and/or forced convection conditions provides for a temperaturegradient or heat dissipation gradient such that more heat is dissipatedfrom an end of the container which is not connected to the source ofgaseous ammonia than from the end connected to the source of gaseousammonia.

A number of advantages are associated with the present inventionincluding

-   -   Good heat transfer from heating source    -   High heat conduction throughout the storage material    -   Heat transfer and conduction not (only slightly) dependent on        storage material properties (and ammonia content)    -   Good mechanical and thermal contact to the heating source    -   Increased mechanical stability of the storage material.        -   Wrapping storage material in foil will reduce degassing of            ammonia during processing        -   Wrapping storage material in foil will reduce problems with            dust during processing        -   During wrapping process the storage material is            pre-compacted        -   Regular shaped packages results in higher storage material            density before pressing        -   Evenly distributed packages results in higher storage            material densities after pressing

Those properties make the compacted block of material of the presentinvention ideally suited for the intended applications where its servesas an ammonia source contained in a container which may be heated and/orbe connected to a vacuum line. Such containers are usually connected,usually via suitable dosing devices, with an ammonia consuming unit,such as an SCR catalyst in an exhaust line of a combustion engine,device splitting ammonia into nitrogen and hydrogen or a fuel cellrunning with ammonia.

FIG. 1 shows a schematic sectional view of a compacted block of material100 in a container 102 optionally comprising a heating source 103 thecompacted block of material 100 being constructed of units or packages104 containing ammonia saturated storage material 106 wrapped into aheat conducting gas-permeable, flexible material 108. As can be seen,the voids or interstices 110 (grossly exaggerated in the drawing) areminimized and the major part of the surface area of the enclosures 108is parallel to the desired direction of heat conductance, which is thedirection of radii originating from the longitudinal axis through thecenter of mass of the cylinder shape of the compacted block of material.

FIG. 2 shows a schematic sectional view of a compacted block of material200 in a container 202 optionally comprising a heating source 203 thecompacted block of material 200 being constructed of one unit or packagecontaining ammonia saturated storage material 206 wrapped into a heatconducting gas-permeable, flexible material 208. In addition to theammonia saturated storage material 206, secondary units or packages 204filled with further saturated ammonia storage material 206′ wrapped intoheat conducting gas-permeable flexible material 208′ are enclosed in theouter enclosure 208.

FIG. 3 a shows a schematic sectional view of non-compressed startingunits 304 containing ammonia saturated storage material 306 wrapped intoa heat conducting gas-permeable, flexible material 308 introduced(“poured”) in a container 302 with large voids or interstices 310.

FIG. 3 b shows the same units after compression by an external force fvia a piston 320 wherein the compacted units 304′ contain compactedammonia saturated storage material 306′ wrapped into the heat conductinggas-permeable, flexible materials 308 the whole assembly forming acompact mass of material 300 in a container 302 with vanishing voids orinterstices 310′.

FIG. 4 a shows a schematic sectional view of non-compressed startingunits 404 introduced (“poured”) in a container 402 with large voids orinterstices 410 between them which contain ammonia-depleted storagematerial 406 wrapped into a heat conducting gas-permeable, flexiblematerial 408

FIG. 4 b shows a schematic sectional view with units 404′ which havebeen expanded by introducing ammonia into the ammonia-depleted storagematerial 406 of FIG. 4 and compacted thereby so as to contain compactedammonia saturated storage material 406′ wrapped into a heat conductinggas-permeable, flexible material 408 the whole assembly forming acompact mass of material 400 in a container 402 with vanishing voids orinterstices 410′.

FIG. 5 shows an example of an automatic packing line for packing ammoniastorage material into foil. In step 1, a piece of foil 508 is placed ontop of shaping tool 504. In step 2. piston 506 is moved downward byactuator 507 into the shaping tool 504 thereby giving the foil 508 abowl shape. In step 3 the bowl-shaped foil 508 is filled with apredetermined portion of ammonia storage material 502 from dosage device510. In step 4 the bowl-shaped foil 508 is pre-closed by a pre-closinginstrument 512, and second pistons 514 and 516 are positioned above andbelow the shaping toll 504. In step 5 the second pistons 514 and 516 areextended, thereby completely closing the foil 508 filled with ammoniastorage material 502, which is then removed from the line, as shown in6.

FIG. 6 shows the temperature/pressure curves of the phase boundary ofliquid ammonia/gaseous ammonia and of the equilibrium pressure ofSr(NH₃)₈Cl₂. It might seem desirable to a person skilled in the art thatthe temperature, T_(T), should be chosen as low as possible toaccelerate the heat removal from the unit, e.g., if water is the coolingmedium, close to about 0° C. (freezing should be avoided). However, ascan bee seen from FIG. 6, at about 0° C. the vapor pressure of liquidNH₃ is rather low, namely about 4.3 bar. Furthermore, the equilibriumtemperature of saturated SrCl₂ at that pressure is about 60° C. At about40° C., the ammonia pressure of liquid ammonia is about 15.5. bar. Thispressure corresponds to an equilibrium pressure of ammonia-saturatedSrCl₂ at a temperature of about 99° C. This means that the SrCl₂ can bepresent at a temperature of about 99° C. (reached e.g. by the exothermicabsorption of ammonia) and be fully saturated at that ammonia pressure.

Example 1

Packages are formed by wrapping 100 g ammonia saturated strontiumchloride in aluminum foils weighing 5.1 g with dimensions 50 μm×194mm×194 mm. 236 packages are pressed into a cylindrical container ofstainless steel with diameter 200 mm and volume 18.7 I with a force of5×10⁶ N. A well connected self-supporting heat conducting structure ofclosed aluminum surfaces is obtained. The resulting density of thesaturated salt was more than 95% of the maximum density obtainable.

Example 2

A container with a volume of 2.24 L is filled with 99 packages eachcontaining 12 g SrCl₂ packed in aluminum foil with a thickness of 50 mmand an area of 12.5×12.5 cm². After saturation the density of thestrontium chloride is 1.0 g/ml.

The content of all patents, patent applications and other literaturecited herein is hereby incorporated by reference in its entirety.

1. A compacted block of material constructed of one or more unitsconsisting of matter comprising an ammonia-saturated material capable ofreversibly desorbing and ad- or absorbing ammonia surrounded by agas-permeable enclosure made of a flexible material having a thermalconductivity of at least five times the thermal conductivity of saidammonia-saturated material at −70° C. to 250° C.
 2. The compacted blockof material of claim 1, wherein said one or more units, in addition tosaid ammonia-saturated material, contain one or more secondary unitsidentical to the units of claim 1 except for being smaller.
 3. Thecompacted block of material of claim 1, which has been compacted bymeans of a pressure of at least about 5 MPa.
 4. The compacted block ofmaterial of claim 3, wherein said compacted block of material isself-supporting.
 5. The compacted block of material of claim 4, whereinsaid compacted block of material is contained in a container whichoptionally may be heated.
 6. The compacted block of material of claim 1,wherein said compacted block of material is contained in a containerwhich optionally may be heated.
 7. The compacted block of material ofclaim 1, wherein said ammonia-saturated material comprises one or moremetal ammine complex salt of the formula M_(a)(NH₃)_(n)X_(z), wherein Mis one or more cations selected from alkali metals selected from Li, Na,K and Cs, alkaline earth metals selected from Mg, Ca, Sr and Ba, and/ortransition metals selected from V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, andcombinations thereof selected from NaAl, KAl, K₂Zn, CsCu, and K₂Fe; X isone or more anions selected from fluoride, chloride, bromide, iodide,nitrate, thiocyanate, sulphate, molybdate, and phosphate ions; a is thenumber of cations per salt molecule; z is the number of anions per saltmolecule; and n is the coordination number of about 2 to about
 12. 8.The compacted block of material of claim 7, wherein theammonia-saturated material is selected from Mg(NH₃)₆Cl₂, Ca(NH₃)₈Cl₂,Mn(NH₃)₆Cl₂ and Sr(NH₃)₈Cl₂ and any mixtures thereof.
 9. The compactedblock of material of claim 7, which has been compacted to such a degreethat the density of the ammonia-saturated material is at least about 70%of its maximum density at normal temperature and pressure.
 10. Thecompacted block of material of claim 1, wherein the thermal conductivityof said gas-permeable enclosure made of a flexible material is at leastabout ten times the thermal conductivity of said ammonia-saturatedmaterial.
 11. The compacted block of material of claim 1, wherein saidgas-permeable enclosure made of a flexible material is selected frommetal, metal alloys, graphite, composite materials, modified plastics,modified rubber and any mixture thereof.
 12. The compacted block ofmaterial of claim 11, wherein said gas-permeable enclosure made of aflexible material is selected from aluminum or an aluminium alloy. 13.The compacted block of material of claim 5, wherein said gas-permeableenclosure made of a flexible material comprises about 0.1 to about 20mass % of the mass of the compacted block.
 14. The compacted block ofmaterial of claim 1, wherein the units of the compacted block ofmaterial have a shape so that at least about 80% of the total surfacearea of said gas-permeable enclosures made of a flexible material isparallel within about ±10° to the desired direction of heat transport.15. A method of producing the compacted block of material of claim 1comprising: wrapping said matter comprising an ammonia-saturatedmaterial capable of reversibly ad- or absorbing and desorbing ammoniainto a gas-permeable, flexible material having a thermal conductivity ofat least five times the thermal conductivity of said ammonia-saturatedmaterial at −70° C. to 250° C. so that one or more units of wrappedmatter are provided, and compressing said one or more units by anexternal pressure of at least about 5 MPa, wherein, optionally, said oneor more units are placed in a container or mold having one or twoopposite open end(s) and optionally one or more removable walls and saidexternal pressure is exerted uni-axial through the open end(s),optionally via a plate.
 16. A method of producing the compacted block ofmaterial of claims 1, comprising: wrapping matter comprising anammonia-depleted material capable of reversibly ad- or absorbing anddesorbing ammonia into a gas-permeable, flexible material having athermal conductivity of at least five times the thermal conductivity ofsaid ammonia-saturated material at −70° C. to 250° C. so that one ormore units of wrapped matter are provided, filling the one or more unitsinto a container, such that the unit(s) are immobilized in thecontainer, and treating the ammonia-depleted material capable ofreversibly ad- or absorbing and desorbing ammonia with ammonia, therebysaturating and compacting the material capable of reversibly ad- orabsorbing and desorbing ammonia.
 17. A method according to claim 16,wherein said saturating and compacting comprises: a. placing the storagecontainer(s) in direct or indirect contact with a thermostatting mediumat a temperature level T_(T)≦about 65° C.; and b. connecting the storagecontainer(s) to a source of gaseous ammonia wherein at least during apart of the saturation process the gaseous ammonia during saturating ofthe ammonia storage material to a predetermined saturation degree is ata pressure P_(S)≦about P_(T), wherein P_(S) is the ammonia pressureduring saturating of the ammonia storage material and P_(T) is theequilibrium vapor pressure of liquid ammonia at the temperature levelT_(T).
 18. A method according to claim 16, wherein the temperature levelT_(T) is of from about 0° C. to about 40° C.
 19. A method according toclaim 17, wherein said thermostatting medium is water or a monophasicaqueous medium.
 20. A method according to claim 17, wherein saidpressure P_(S) is at least about 50%, of the equilibrium vapor pressureof liquid ammonia at the temperature T_(T).
 21. A method according toclaim 17, wherein said predetermined saturation degree is at least about80% of the theoretical full saturation.
 22. A method according to claim17, wherein the part of the method where the gaseous ammonia is at apressure P_(S) which is lower than or equal to the equilibrium vaporpressure P_(T) of liquid ammonia at the temperature T_(T) is the finalpart of the method during about the last about ⅓ of the total saturationperiod or wherein the last about 25% of the predetermined saturationdegree is achieved.
 23. A method according to claim 17, wherein thecontainer is in direct or indirect contact with the thermostattingmedium in its entirety.
 24. A method according to claim 17, wherein onlya part of the container is in direct or indirect contact with thethermostatting medium
 25. A method according to claim 17, wherein thedirect or indirect contact with the thermostatting medium is increasedwith increase of saturation or re-saturation by raising the level of thethermostatting medium in a thermostatting bath in which the container isimmersed, starting from the end of the container which is not connectedto the source of gaseous ammonia to the end connected to the source ofgaseous ammonia.
 26. A method according to claim 17, wherein the end ofthe container connected to the source of gaseous ammonia is insulatedsuch that about 50% or less of the surface of the container is coveredwith an insulating material during at least a part of saturation orre-saturation time.
 27. A method according to claim 17, wherein acooling device and/or other temperature controlling device and/or forcedconvection conditions provide for a temperature gradient or heatdissipation gradient such that more heat is dissipated from an end ofthe container which is not connected to the source of gaseous ammoniathan from the end connected to the source of gaseous ammonia.